The invention relates to a lining (brake pad) wear adjustment device for a disc brake, in particular for a motor vehicle, having a brake application device with a brake actuating lever. The wear adjustment device can preferably be inserted into an adjustment spindle of the disc brake. The invention also relates to a method for controlling the lining wear adjustment device and to a corresponding disc brake.
Lining wear adjustment devices of this type are known in different embodiments such as, for example, mechanical adjusters with automatic adjustment of a friction point. In this context, every time the brakes are actuated, the wear adjustment device is activated, for example by an actuating lever of a brake application device of the disc brake. In the case of wear on brake linings (brake pads) and the brake disc, automatic adjustment of the linings occurs by means of the adjustment device, for example by means of an adjustment movement of longitudinally variable thrust spindles.
EP 1 476 673 B1 describes a disc brake with an adjustment device which is driven by an electric motor and a method for controlling a disc brake.
These known arrangements have proven effective.
The object of the present invention is to provide an improved lining wear adjustment device for a disc brake. A further object is to provide an improved disc brake.
This and other objects are achieved by a lining wear adjustment device having a brake application device with a brake actuating lever. The wear adjustment device can preferably be inserted into an adjustment spindle of the disc brake. The wear adjustment device includes an adjustment shaft having an external bearing, a rotary drive element, and a clutch device for controllably coupling the rotary drive element to the adjustment shaft, wherein the clutch device is configured to be an electrically controllable solenoid clutch having at least one electromagnetic coil.
The lining wear adjustment device has the clutch device configured so as to be electrically controllable with the at least one electromagnetic coil. An existing brake actuating lever is used to provide a drive. The transmission of the torque, brought about by this brake actuating lever, to an adjustment spindle can be controlled easily by a switch by way of the controllable clutch device.
The brake lining/linings can be adjusted as an actuation process on the basis of wear but also as a resetting process. It is therefore possible to set a so-called clearance between the brake lining and the brake disc. Resetting is possible if the clutch device is switched on during a return movement of the brake actuating lever.
A lining wear adjustment device according to the invention for a disc brake, in particular for a motor vehicle, having a brake application device with a brake actuating lever, can preferably be inserted into an adjustment spindle of the disc brake. The wear adjustment device includes an adjustment shaft having an external bearing, a rotary drive element, and a clutch device for controllably coupling the rotary drive element to the adjustment shaft. The clutch device is designed as a solenoid clutch which is electrically controllable with at least one electromagnetic coil.
A method is provided according to the invention for controlling the lining wear adjustment device of a disc brake, in particular for a motor vehicle, having a brake application device with a brake actuating lever and at least one adjustment spindle. When lining wear is detected, adjustment takes place after a presettable comparison value has been reached by energization of the electromagnetic coil of the clutch device during adjustment of the brakes by the brake actuating lever.
According to one embodiment, the clutch device includes at least one section of the rotary drive element and/or a section which is connected in a rotationally fixed fashion to the rotary drive element, a clutch cover, the at least one electromagnetic coil and a coil carrier. As a result, a compact design becomes possible.
There is provision that the rotary drive element is arranged on an input side of the clutch device so as to be pivotable about a common axis of the adjustment spindle and of the clutch device and to be axially displaceable. Alternatively, the section which is connected in a rotationally fixed fashion to the rotary drive element can be axially displaceable, wherein the rotary drive element then just carries out a pivoting movement.
In this way, the rotary drive element can be pivoted by the brake actuating lever without actuation taking place. The torque is transmitted to the adjustment spindle only if the clutch device is switched on, wherein the rotary drive element is displaced axially into the engagement position of the clutch device when the clutch occurs.
According to one embodiment, the coil carrier is connected in a rotationally fixed fashion to the rotary drive element. A compact design is therefore possible, wherein the electromagnetic coil can be pivoted with the rotary drive element.
According to an alternative embodiment, the coil carrier is fixedly connected to the external bearing of the adjustment shaft. The electromagnetic coil does not pivot during an adjustment process. Through a suitable selection of materials for the coil carrier, the magnetic force lines of the electromagnetic coil can be advantageously influenced in the switched-on state, in order to keep a leakage field as small as possible and bring about a strong clutch force.
According to a further alternative embodiment, the coil carrier has a disc section with a shell receptacle which is spherical in the central region. The spherical shell receptacle receives a spherical projection of a disc of the external bearing of the adjustment shaft and corresponds to the spherical projection of the disc of the external bearing. It is then advantageously possible for an angular movement of the lining wear adjustment device to be compensated during actuation.
According to a further embodiment, the clutch cover surrounds the electromagnetic coil in a pot shape, is connected in a rotationally fixed fashion to the adjustment shaft and has a clutch region which forms a clutch section with a section of the rotary drive element or with a section which is connected in a rotationally fixed fashion to the rotary drive element. A compact design of the entire lining wear adjustment device can be made possible by drawing in sections of the rotary drive element.
According to one embodiment, the clutch section is embodied with friction linings. They can be designed, for example, as a coating or provided as additional parts.
According to an alternative embodiment, the clutch section is design as a toothed clutch. The clutch section, which is designed as the toothed clutch, can have an oblique angle, wherein this angle can be, for example, in the range of 20°. The clutch forces can therefore be kept small in the coupled state, wherein the electromagnetic coil takes up a correspondingly small amount of space.
According to a further embodiment, the clutch device is provided with at least one release or resetting spring. An uncoupled or released state of the clutch device is therefore ensured even in difficult environmental conditions, for example temperature differences and/or vibration.
To compensate for angular movements of the adjuster, according to one alternative embodiment the external bearing can be designed with a cardanic bearing of the adjustment shaft.
The lining wear adjustment device has a connection device which is connected in an electrically conductive fashion to the at least one electromagnetic coil. The electromagnetic coil is connected electrically by use of a plug-type connection. This makes it possible to change the connection device easily and quickly in the case of maintenance or replacement without, in particular, electrical connections having to be released or produced by use of tools.
According to another embodiment, the plug-type connection has conductors which are guided through the external bearing by use of an elastic securing device and are secured in the external bearing. As a result, stresses and movements during the actuation of the lining wear adjustment device can be compensated. The electromagnetic coil is connected to the conductors.
According to a further embodiment, the lining wear adjustment device has at least one lining wear sensor. It is therefore possible to carry out an adjustment process in a targeted fashion as a function of the wear of brake linings and the brake disc by virtue of the fact that the clutch device is correspondingly switched on and off
According to another embodiment, the at least one lining wear sensor is at least partially a component of the connection device. A particularly compact and simple design is therefore possible.
It is particularly advantageous if the at least one lining wear sensor is embodied as an angle sensor, wherein a wear sensor element is arranged in the connection device and interacts with a wear encoder element which is connected to the adjustment shaft. In this context, the wear sensor element can be, for example, a Hall sensor, wherein the wear encoder element can be a permanent magnet. It is advantageous here that an effect of the permanent magnet on the sensor element occurs via a wireless magnetic field. Therefore, for example, separate mounting of the wear sensor element in the connection device and wear encoder element on the adjustment shaft is possible, which facilitates replacement and maintenance work and, in particular, adjustment work.
According to yet a further embodiment, the lining wear adjustment device has at least one actuating lever sensor. The adjustment lever sensor can be designed as at least partially a component of the connection device and also as an angle sensor. In this context, as in the case of the lining wear sensor, an adjusting sensor element can be arranged in the connection device and can interact with an actuating encoder element which is coupled to the brake actuating lever.
As in the case of the lining wear sensor, it is also highly advantageous here if the actuating encoder element is a permanent magnet. The number of spare parts is reduced through the selection of identical sensor elements and encoder elements. Furthermore, identical components and evaluation programs are used to evaluate and connect the sensor elements.
According to a further embodiment, the connection device can have a control unit. Retrofitting of existing disc brakes is therefore possible since, for example, previous electromechanical potentiometers can be modeled electronically, wherein existing connections of a potentiometer on a control unit can continue to be used by the modeled connections, for example by use of the control unit.
According to yet a further embodiment, the clutch device has at least one anti-rotation device. This can be achieved, for example, by way of separate friction faces on the components of the clutch device and external bearing together with force accumulator elements, for example pressure/tension springs. A reliable securing force and robust design are therefore obtained.
According to a further embodiment of the method, the electromagnetic coil is energized as a function of a detected movement of the brake adjustment lever. This is possible if a combination of a lining wear sensor and actuating lever sensor is present in the lining wear adjustment device.
According to yet a further embodiment, a friction point can be detected by the frictional engagement of the adjustment spindle in that the actuating movement of the brake actuating lever and an adjustment movement of the lining wear adjustment device are detected. If an adjustment movement occurs at the same time as an actuating movement of the brake actuating lever and is then no longer present despite a further actuating movement, the friction point is reached. This may also be the case if no adjustment movement occurs at the start of an actuating movement.
According to yet a further embodiment, the lining wear adjustment device is reset by a presettable value by a return movement of the brake actuating lever by energizing the electromagnetic coil when the brake lining bears against the brake disc without brake application tension and grinds. Such bearing and grinding can be detected, for example, by a temperature sensor.
It is also possible to reset the brake lining/linings into its/their home position by return movements of the brake actuating lever with simultaneous switching on of the clutch device, which is necessary for example, for replacement and maintenance.
A disc brake having a brake application device with a brake actuating lever and at least one adjustment spindle has at least one lining wear adjustment device as described above.
By way of the lining wear adjustment device, not only lining wear adjustment but also lining resetting, for example in the case of a fault or in the case of replacement and maintenance, are possible, using the clutch device with the electromagnetic coil, in other words with an electromagnetic clutch. In this case, so-called clearance setting is also easily possible. The drive source here is the brake actuating lever as before in the case of mechanical adjustment devices.
Furthermore, a so-called stand-alone version is possible which can be retrofit into existing series-mounted brakes.
The lining wear adjustment device has a connection device which, in one version, makes available an analog signal of the lining wear sensor and of the actuating lever sensor (if used). For this purpose, the connection device has a control device, for example a microcomputer or small processor. The connection device can, however, also transmit the sensor signals in a digital fashion without a control device to the superordinate control unit with a corresponding control device.
When a failure of the electrical brake (for example, failure of a 5 V supply voltage of a potentiometer) is detected, the tracking of the brake system can be ensured. This is done by actuating the electromagnetic coil after it has been detected that the clearance has been closed, as long as the brake still actuates, but not when the brake is released.
The stand-alone version is compatible with previous embodiments and can therefore be replaced for the purpose of retrofitting.
The lining wear adjustment device also has the following advantages:                Autonomous electrical lining detection and adjustment        Analog outputting of lining wear        High possible torque for adjusting by use of a toothed clutch        Reliable securing force by means of one, but preferably two, friction faces (ramp toothing systems are also possible instead of friction faces)        Simple robust design        Independent supply voltage        Lining wear adjustment even in emergency operating mode of the brake (back-up).        
The lining wear adjustment device can additionally have an overload clutch, for example a ball ramp clutch or oblique toothing system.
The electromagnetic coil can also be energized by way of PWM or some other suitable actuation processes. It is therefore possible, for example, to obtain a settable overload clutch.
The electromagnetic coil is provided with connection wires of a line which is connected to a plug-type connection. In this context, the connection wires can be stranded conductors or conductor tracks of a flexible circuit board which, through their flexibility, can compensate angular movements when the lining wear adjustment device is actuated.
Furthermore, it may be possible for the connection device to be provided with signal processing for a rotational speed signal of a rotational speed sensor of the associated wheel. In this context, the rotational speed sensor can also be connected to the connection device, wherein its rotational speed signal can be processed in such a way that it can be transmitted in a common cable from the disc brake to the control unit for evaluation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.